Learn how to decode the indexing system for coding similar-sounding surnames.

The 1880, 1900 and 1920 federal censuses, plus parts of the 1910 and 1930 censuses, are indexed by state using a code based on the sounds in your ancestors' surnames. This indexing system — called Soundex — is especially useful when you don't know specifically where the family was living in the census year. The family's Soundex card will tell you their county and community, and where you can find their names on the census. Soundex most often is available as microfilm of the cards on which basic census information was written. Names with the same code appear together in the Soundex. (Note that the 1880 Soundex includes only households with children ages 10 and under.)

The system works like this: Letters with similar sounds have the same code (see the key at right). The code begins with the first letter of the surname. Of the remaining letters, cross out all vowels (a, e, i, o and u) plus w, h and y. With the consonants, form a three-digit code. For Carpenter, the code begins with C. Cross out a, e, e, and code r as 6, p as 1, n as 5. Disregard the remaining letters. The code is C615.

Code as one digit any double letters, such as tt or rr (Saddler — S346), or consonants with the same code that occur together, such as ck or sc (Scanlon — S545). Names with h or w between same-code letters are coded as if the h or w was not in the name at all (Sachse — S200, not S220). If you run out of key letters before you have the required three digits, simply add zeros (Mott — M300; Lee — L000). Names with the same code appear together in the Soundex.